How Soy Supplements May Affect Breast-Cancer Genes

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Taking soy protein supplements may lead to some concerning
genetic changes for women with breast cancer, a new study
suggests.

In the study, half of 140 women diagnosed with invasive
breast cancer took soy protein powder and the other half took
a placebo for between seven and 30 days before they had surgery
to remove their cancer. The researchers compared tumor tissues
from before and after surgery, and found changes in the
expression of certain genes that promote cell growth among women
in the soy group and that could potentially accelerate breast
cancer progression.

"These data raise concern that soy may exert a stimulating effect
on breast cancer in a subset of women," the researchers wrote in
Sept. 4 issue of the Journal of the National Cancer Institute.
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However, the researchers do not know if these changes in the
expression of some of the genes are reversible, said study author
Dr. Jackie Bromberg, a breast cancer oncologist at Memorial Sloan
Kettering Cancer Center in New York.

"We do not know what the consequences of taking soy for longer
[periods] or taking higher amounts of soy, would have on the
biology of a breast tumor," Bromberg said. The study also did not
look at the effects of soy on preventing breast cancer.

Additionally, the researchers did not observe any changes in the
tumor's rate of growth as a consequence of soy, Bromberg said.

The researchers cannot extrapolate their findings to suggest that
taking soy is 'good' or 'bad' for women, Bromberg said.

In the study, conducted between 2003 and 2007, almost 61 percent
of women were postmenopausal, and their average age was 56-
years-old. The women were instructed to take two packets
containing 25.8 grams of protein powder a day, or a placebo.

Previous research on the relationship between
soy supplementation and breast cancer has yielded conflicting
results. For example, some studies in Asian populations have
shown that soy consumption was related to a lower risk of breast
cancer incidence and recurrence, the researchers said. However,
soy intake was unrelated to breast cancer risk in a number of
other studies in western populations. Still, patients with breast
cancer are often advised to avoid soy foods, the researchers
wrote.

"I think the study provided preliminary evidence that soy
supplementation can affect gene expression in breast tumors,"
said Dr. Michael S. Cowher, an associate staff and quality
improvement officer at Cleveland Clinic's Breast Services, who
was not involved with the study. "However, evidence is still
lacking on any outcomes" of this change in gene regulation when
it comes to the patients' survival, recurrence of breast cancer,
or response to therapies such as chemotherapy, Cowher told Live
Science.

"We still don't know whether or not soy supplementation is
beneficial or harmful to patients with breast cancer," Cowher
added.

"For the individual patient with breast cancer, soy intake is
part of the discussion to have with your doctor regarding
potential modifications," Cowher said. "I generally advise
both patients with and those at higher risk for breast cancer to
avoid excessive soy intake, but remind them that it is possible
that future research will find that for some patients soy
supplementation may be beneficial, while harmful to others."